Sleep training and relatives

I'm getting really pissed off my fiance's side of the family comparing my 8 month old to her now 18 month old cousin. She still sleeps with a parent in bed and the other parent in seperate room. When I mentioned to my fiance I will start sleep training, he soon pointed his niece as the example. I said no way, a child needs their own bed and we as a couple need ours. At my in-laws and LO starts crying because it's time for her sleep but fights it when she's elsewhere, so my FIL insisted my LO is hungry (even though she ate) because his other grandchild never acted this way her age. Just like WTF! I let it slide because I don't care to deal with ignorance but later on I'm so turned off I don't care to see them for a longgggg while. I'm going to be honest and say my SIL is a sneaky bitch and her husband is a vile judgmental wannabe who bad mouths her entire family at his work. I must say I don't want anything to do with them or be compared to such snots.